Bourdon tubes and like resilient, pressure-responsive tubular elements



July 5, 1955 c. H. BOOTH 2,712,240

BOURBON TUBES AND LIKE RESILIENT, PRESSURE-RESPONSIVE TUBLAR ELEMENTS Filed sept. 25, 1955 2 sheets-sheet 1 2,712, 240 IVE C. H. BOOTH July 5, 1955 KE RESILIENT, PRESSURE TUBLAR ELEMENTS -RESPONS BOURDON TUBES AND LI 2 sheets-sheet 2 Filed Sept. 25. 1953 United States Patent O BOURDON TUBES AND LIKE RESILIENT, PRES- j SURE-RESPONSIVE TUBULAR ELEMENTS Christopher Hodgson Booth, Bath, England Application September 25, 1953, Serial No. 382,419

Claims. (Cl. 7-3-418) Y This application is a continuation-in-part of my abandoned application Serial No. 159,604 tiled May 2, 1950.

The invention relates to pressure responsive units for use in pressure responsive instruments and comprising a resilient, pressure responsive, tubular element of the kind (usually designated Bourdon tubes) in which the element is arranged to flex laterally (i. e. transversely to its length) under changing internal and external pressurediiferences, the element being closed at one end and also comprising means at the other end for connecting the element to a source of pressure. ments for use in such units. Such elements as at present constructed are of curved form and usually of somewhat attened cross-section and are used, for example, as the operating members in pressure indicating instruments, the iexing movements of the elements being employed to operate the indicating mechanism.

It is an object of the invention to provide elements of the above kind which are capable of considerable flexing movement without being permanently deformed and which require very little change in' internal volume for a substantial lateral llexing movement.

According to the invention a pressure responsive unit of the above kind comprises an element which is of strip like formation and comprises two tlexible strips in faceto-face relationship and secured to each other along at least two laterally spaced longitudinal seams thereby forming an elongated tube betweenthe seams at in crosssection, a pressure tight closureat one end of the tube and means at the other end for connecting the tube in pressure-tight relation to a source of pressure, the tube being constructed to llex transversely to its length and having one end free for movement by such llexing of the tube.

In one form of the invention the element is composed of two metallic strips secured as aforesaid (e. g. by welding, brazing or soldering) face-to-face along or adjacent to their edges and, it may be, also intermittently intermediate in their width. The strips may be securedintermediate in their width by spot welding, for example, in one or more (say three) longitudinal rows, the welds preferably being staggered between the several rows when there are more than one.

The elements used in the invention will normally be of curved form in accordance with the present practice but they may be straight in which case the opposed walls of the element will have diierent resistances to bending, for instance, they may be composed of strips of different thicknesses or of different materials.

For some purposes (e. g. when it is desired to operate an alarm should the temperature of a medium of which the pressure is being measured, rise excessively) it is required that a pressure responsive element of the above kind should also be responsive, by llexing, to changes in temperature. The invention, in one of its forms, meets this requirement by employing, for the strips, materials having different coeilcients of thermal expansion whereby on change of temperature one strip will expand, or con- The invention also relates to ele- 2,712,240 Patented July 5, 1955 tract, more than the other and cause the element to ilex.

and susceptible to work-hardening.

Some preferred constructions of pressure responsive units andthe method of making them will be described by way of example of the invention, and with reference to the accompanying drawings in which:

Figure 1 is a side elevation of one unit,

Figure 2 is a front view of a tubular element used in the unit, in course of construction,

Figure 3 is a detail view of the end of the completed unit,

Figure 4 is a section on the line IV-IV in Figure 3,

Figure 5 is a view, corresponding to Figure 2 `of an alternative form of element which may be used in the unit shown in Figures l to 4,

' Figure 6 is a view, corresponding to Figure l of a second form of unit,

Figure 7 is a section, 6, and Y Figure 8 is a side elevation of a third form of unit.

The unit shown in Figures l to 4 comprises a tubular element 1 consisting of two thin strips 2, 3 of austenitic stainless steel of a welding quality or of beryllium copper or other material which, preferably, is readily weldable The strips are secured face to face and joined along their edges 4 by brazing or resistance welding, the side joints being made pressure-tight and of a width to provide a joint strength equivalent to that of the strips. In addition to the continuous side joints -the two strips are also joined together by spot welding at frequent regular intervals along three longitudinal rows 5 intermediate in the width of the element. Y

After the strips have been secured together they are subjected to work-hardening by a rolling operation which reduces the thickness of the element and increases its hardness and elasticity.

After being cut to the length required the tube is secured at'one end to a suitable holder 8 providing connection means for introducing pressure into the interior of the tube, the tube being secured to the holder by low temperature soldering so as not to affect the elasticity of the tube. The free end of the tube is closed by soldering into a suitable block 9 with two air escape holes at the corners'at the end of the tube. To ensure that the solder does not seal the ends of the tube from the air holes and holder connection, strips 10 of aluminium foil are inserted into the ends of the tube before soldering. The air is then expelled (e. g. by application of hydraulic pressure t0 the element) and the holes are closed by screws 11 to make a pressure-tight joint. The block has a screwed stop 12 for operating an indicating device according to the movements of the block under changing pressure within the tube.

on the line VII-VII, in Figure Finally the tube is shaped by bending to the curved i form required and `subjected lto fluctuating hydraulic pressures for the purpose of ageing the tube.

Figure 5 shows an alternative form of tube which may be used in the element described above. In this tube the rows 5 of intermediate welds are omitted, the tube being intended for use under conditions in which the strips themselves have sulcient stiffness to prevent undue separation of the strips under the internal pressure. A further feature of this tube, which may also be embodied in that described above, is that the weld seams 4A are spaced inwardly from the edges of the strips to leave marginal portions 15. It is an advantage of this feature that the stiffness of the tube may be reduced after manufacture (e. g. for calibration purposes) by removing (e. g. by grinding) a part or the whole of the marginal portions.

If it is desired that the element shall be responsive to temperature changes, the two strips 2 and 3 are made of metals having different coeliicients of thermal expansion e. g. the alloy known under the name Invar and brass, bronze or steel respectively. An element made in this way responds, at least to some extent, like a conventional bi-rnetailic strip and is also responsive to pressure changes as described above. 1t has been found that the response to temperature changes is greater when the tube has intermediate welds as in the first example.

Should it be desired that movements of the element in response to changing internal pressures be transmitted over a distance an electric strain indicator of weil known type may be secured to the inside surface of the element as indicated at 14 in Figure l and the varying electrical characteristics of the indicator be employed to transmit signals to a distant electrically responsive indicator.

Figures 6 and 7 show a forni of unit which is responsive to variations in the sum of two pressures. The unit has a tubular element which is constructed of three strips 20, 21, 22 secured together along their edges and by spot welding as described above. The two pressures whose sum is to be indicated are admitted between the. strips 20 and 21. and the strips 21 and Z2 respectively and the-element exes according to the sum of these pressures. The element is secured at one end in a holder 24 having pressure inlet connections 25, 26 leading to the two tubes respectively and to be connected to the twoA pressure sources of which the sum is to etect the flexing of the element. The other ends of the tubes are closed by a block 27 having bleed holes on its opposite sides for the two tubes respectively and closed by screws 28.

In Figure 7 there is shown a form of pressure responsive unit which has a tubular element 30 of straight form. The element is constructed, as above described, of two strips 31, 32 which, in this example, are of different thicknesses and consequently have different resistances to exing.

In order to obtain maximum exibility, within the elastic limit of the material employed in an element of the kind with which the invention is concerned, it is animportant consideration that the element shall be as thin as possible. The element provided by the present invention meets this consideration in that it is of strip-like formation and may be constructed of thin material while at the same time the feature of securing the walls of the element. intermediate in the width may be used when necessary to ensure that the element will resist internal pressure tending to separate the walls and` so to alter the ilexibility of the strip and eventually to burst it.

The invention includes a pressure responsive device (e. g. a pressure gauge or a pressure controlling device) incorporating as its pressure responsive member a unit constructed as described above. The unit may for example be used in an indicating device as described in my copending application Serial No. 159,603 tiled May 2, 1950 in which case the screw 12 described above will constitute the operating stop (i. e. the screw 26) described in that application or, also as described in that application, the free end of the element, appropriately shaped, may engage in a helical groove in an operating.

spindle carrying a pointer or the equivalent.

I claim: l

l. For use in a pressure responsive instrument, a pressure responsive unit comprising a tubular element capable of flexing transversely to its length under changing internal and external pressure differences and comprising two exible strips in face-to-face relationship and secured to each other along two laterally spaced longitudinal seams thereby forming an elongated tube between the seams at in cross-section and further secured together intermittently intermediate in the width of the strips, between the seams, thereby preventing substantial separation of the strips under internal pressure within the working range of the element, a pressure tight closure at one end of the tube and means at the other end for connecting the tube in pressure-tight relation to a source of'pressure, the tube being curved about at least one axis transverse to its length and having one end free for movement, by flexing of the tube.

2. A pressure responsive unit as claimed in claim l in which the strips are of metal and the seams are formed by welds between the faces of the strips.

3. A pressure responsive unit as claimed in claim l in which the strips are of metal andare secured together intermittently intermediate in the width. of the strips, as aforesaid, by welds.

4t A pressure responsive unit as claimedA in claim l in which thev strips are of metal and are secured together intermediate in the width of the strips, as aforesaid, by at least two longitudinal rows of spot welds, the welds being. staggered between the several rows.

5. In a Bourdon tube of the type comprising a curved` tube substantially flat in cross-section, sealed at one end thereof and at its other end adapted to be connected to a source of pressure, the improvement comprising means securing the at wall-portions of the tube together at at least one point spaced. from the sides and ends of the tube, whereby to prevent separation of the said wallportions ofv the tube.

References Cited in the le of this patent UNITED STATES PATENTS 1,676,923 Phelan et al. July 10, 1928 1,779,911 Little, Ir. Oct. 28, 1930 1,821,669 Rudolph Sept. l, 1931 1,913,239 Ibbott June 6, 1933 2,174',7l Wasson et al. Sept. 26, 1939 2,222,259 Hoffmann et al Nov. 19, 1940 2,390,643 De Beaumont Dec. Il, 1945 2,470,714 Nevius May 17, 1949 FOREIGN PATENTS 12,889 Great Britain `lune 5, 1850kv 1849 2,383 Great Britain Mar. 28, 1864 

